The present invention relates to an electronic device typified by blade servers which have been going to prevail rapidly in recent years, and more particular, to a thermal connector suited to be used in such electronic device, and an electronic device using the same.
Blade servers are offered in a state, in which blades having devices such as CPU (Central Processing Unit), a memory, a hard disk, etc. are loaded into a rack on which a power unit, a fan unit, a management module, etc. are mounted. In particular, the invention relates to a thermal connector between a heat pipe, through which heat of CPU is taken out from a blade, and a heat release device, from which heat taken out through the heat pipe is further discharged outside a rack.
In blade servers which have been rapidly increased in demand in recent years, further improvements in information processing capability and space-saving have been demanded. The information processing capability, however, has been spectacularly improved year by year accompanying with increase in performance of CPUs themselves. Further, an improvement in information processing capability per blade is achieved by increasing the number of CPUs mounted on a single blade. In addition, the number of blades which are mountable on a single rack is increased by thinning the blades. Due to an increase in amount of heat generation accompanied with improvements in performance of CPUs and thinning of blades, power density (heat generation density) of blade servers are spectacularly increased. Therefore, an improvement in cooling efficiency of servers is intensely desired.
Also, “redundancy design” and “maintenance during operation” realize high reliability of blade servers. In “the redundancy design”, the structure of a blade server is designed such that devices, which fulfill the same function, are mounted in larger number than that essentially needed and a device having gone wrong can be covered by another device, which fulfills the same function. Also, in “the maintenance during operation”, a maintenance work in the case where a device in a blade server goes wrong is performed without cutting off a power source of the blade server, whereby the server is prevented from being decreased in operating efficiency. In order to realize the maintenance during operation, it is required that respective units such as blades, or a power source unit, a fan unit, etc. can be mounted to and dismounted from a rack while a blade server operates. This is called hot-swap and characteristic of a blade server. Therefore, it is also required that a cooling device mounted on a blade be detachable.
Hereupon, a typical structure of a blade server will be described. A blade server includes several chassis mounted in a rack. Blades, power source units, fan units, management modules and communication modules are mounted in a chassis. Blades, fan units, and communication modules, respectively, are connected to management modules through a backplane. Electronic parts such as CPU, a memory, a chip set, a hard disk, etc. are mounted on a blade.
Presently, a mainstream cooling method comprises using a fan unit mounted on a chassis to flow air in a blade to cool respective electronic parts. A heat sink formed from a material, such as copper, aluminum, etc., having a high, thermal conductivity is mounted to a CPU, which is larger in heat generation amount among electronic parts. A heat sink mounted to a CPU has been larger in size year by year accompanying with increase of the heat generation amount of CPUs, and has been made high in performance by employing a heat pipe, for example.
However, by virtue of CPUs being spectacularly increased in heat generation amount and blades being thinned, measures of mounting a heat sink to a CPU to perform air-cooling in a blade approaches a limit.
Hereupon, a cooling system is conceivable, in which a heat transport device using a liquid loop and a heat transport device using evaporation are used to transport heat generated from a CPU outside a blade to dissipate heat. With this cooling system, a large-sized radiator or chiller is applicable as heat dissipate means outside a blade, so that it is possible to accommodate for a high heat generation amount of a CPU. On the other hand, the cooling system involves a problem of realizing hot-swap. As means for solving this problem, there is a method of using a coupler to connect between a heat transport device in a blade and a heat transport device outside a blade. However, this method involves a danger of liquid leakage since refrigerant liquid circulates through the coupler between the heat transport device in a blade and the heat transport device outside a blade.
In order to prevent the liquid leakage, it is desirable that the heat transport devices in a blade and outside a blade be completely closed. In this case, there is a need for a thermal connector for connection between the heat transport device in a blade and the heat transport device outside a blade with a small heat resistance.
Subsequently, there is cited a well-known technology with respect to a thermal connector. That is, JP-A-2000-13064 discloses an accessory and an electronic device using a thermal connector for cooling. Also, JP-A-2001-91174 discloses a connector used in electronic devices, industrial machinery, etc. to be detachable and to transport heat. Further, JP-A-2000-356484 discloses a heat-pipe thermal connector capable of detachably connecting between a heat pipe and a cooled member without an increase in heat resistance. JP-A-8-116005 (Japanese Patent No. 3395409) discloses a structure, in which fins for cooling a heat generating element and fins fixed to means for heat release to an outside are brought into contact with each other and a heat conducting medium is made present on contact surfaces.
A method for cooling the accessory described in JP-A-2000-13064 is one, in which heat generated in the accessory is transported to the electronic device through the thermal connector to be dissipated. However, a specific structure of the thermal connector is not disclosed.
The heat transfer connector described in JP-A-2001-91174 comprises a first connector member having a reception part, which is concave-shaped in section, a second connector member having an insertion part, which is convex-shaped in section, and a comb-shaped contact interposed between the first connector member and the second connector member to transfer heat. Both the connector members and the comb-shaped contact, respectively, are formed from a metallic material of favorable thermal conductivity. When both the connector members are connected to each other, the comb-shaped contact is elastically deformed following the reception part of the first connector member and so the solid bodies come into contact with each other to transfer heat therebetween.
Because of a system, in which the solid surfaces come into contact with each other to transfer heat therebetween, however, it is difficult in some cases to achieve a decrease in heat resistance due to influences of machining accuracy (surface roughness, waviness, etc. of tapered surfaces) of surfaces in contact with each other.
With the heat-pipe thermal connector described in JP-A-2000-356484, a heat pipe is inserted into a semi-cylindrical receiving portion to be pressed down whereby the heat pipe and the receiving portion are brought into contact with each other to transfer heat therebetween.
Because of a system, in which the heat pipe is inserted axially into the receiving portion, however, it is difficult to form a structure, in which the heat pipe and the receiving portion are brought into close contact with each other, so that a contact area being effective for heat transfer becomes small to make it difficult to achieve a decrease in heat resistance.
Also, as measures of improving a thermal connector, in which solid surfaces come into contact with each other to transfer heat, in heat transference, a heat conducting medium such as grease, oil, or the like is interposed between the solid surfaces in some cases. When a heat conducting medium such as grease, oil, or the like is used in an opened space over a long term, there is caused a problem that volatile components contained in the heat conducting medium diffuse in an outside air to lead to deterioration.
JP-A-8-116005 discloses a structure, in which oil is filled to improve the heat transference between comb-shaped contact heat transfer members and an oil filled space is closed to prevent oil deterioration. With the conventional technology disclosed in JP-A-8-116005, however, a semiconductor module cannot be exchanged unless a closed device is disassembled after the device is stopped and oil is removed, so that only a part of blades cannot be pulled out or inserted to be exchanged while the whole server remains in operation. That is, hot-swap, which characteristic of a blade server, becomes difficult.
In summary, in an electronic device, such as a blade server, in need of hot-swap, it is problematic to make measures against deterioration of grease and hot-swap compatible with each other in case of using a thermal connector, in which a heat conducting medium such as grease is present.